Myopia results from psychological imperfections in the eye of the patient which cause the focusing of the images in front of the retina. Surgical operations to correct myopia have typically involved techniques for effectively flattening the corneal surface in order to cause a posterior displacement of the focal point.
Hyperopia results from the physiological imperfections causing the focusing of images behind the retina, and a surgical technique used to correct this condition necessarily seeks to alter the patient's eye so as to achieve an interior displacement of the focal point.
Refractive corneal surgery for the correction of myopia is commonly referred to as a radial keratotomy. In this procedure a series of radial incisions are made in the cornea extending from the edge of the pupil outwardly to the limbus. These incisions serve to weaken the cornea causing intraocular pressure to displace the cornea so that the surface of the cornea flattens. Unfortunately, clinical results with this procedure have been characterized by significant variability of results.
An alternative refractive corneal surgical procedure for the correction of myopia has been developed where an annular wedge-like cut is made into but not completely through the cornea around a 360.degree. path between the pupil and limbus. The cut walls are sutured together, causing a carefully controlled flattening of the corneal surface without structurally weakening the cornea or exposing the internal content of the eye to infection.
U.S. Pat. No. 4,807,623 to Lieberman discloses a trephine which is complex and provides for numerous adjustments of the blade. The device relies on a suction ring connected to the base to secure the device during surgery.
U.S. Pat. Nos. 4,750,491 and 4,763,651 to Kaufman et al. disclose a trephine of simple construction comprising a fixation member and two shafts each of which have a blade mounted thereon. The device relies on pressure applied by the user to control the depth of the incision and includes structure obscuring the incision. The fixation member relies on teeth to engage the sclera of the eye to secure the fixation member during surgery.
U.S. Pat. No. 4,336,805 to Smirmaul discloses a trephine containing a flexible drive shaft, ring gear and a drive pinion gear, increasing the size of the trephine and the difficulty of use, in addition to the requirement of operating a trephine with one hand while operating the device via the flexible drive shaft.
U.S. Pat. No. 4,190,050 to Bailey discloses a trephine which is power driven and relies on a vacuum source to secure it to the cornea. A blade is detachably connected to the handle so that it may serve as a storage container for a cornea. The requirement of the power source to operate the trephine decreases its portability, efficiency and increases the difficulty of use during surgery.